Method for reclaiming used foundry sand



March 5, 1957 P. C. WILL ETAL.

METHOD FOR RECLAIMING USED FOUNDRY SND Filed Feb. l, 1954 Il NE frzdnZZ/j' Phi/flip c. .zz/ZZ Rog L. Lace nited States Patent O F -METHOD FOR RECLIMING USED FOUNDRY AND Phillip C. Will, Oak Park, and Roy L. Luce, Chicago, Ill., assignors to The Hydro-Blast Corporation, Chicago, Ill., a corporation of Illinois Application February 1, 1954, Serial No. 407,446

3 Claims. (Cl. 22-217) This invention relates to a method for reclaiming used foundry sand, such as core sand. YThis sand is mixed with a suitable binder consisting of clay and/or organic materialto form a plastic mixture that is capable of being formed into, and retaining shapes imparted thereto. In making foundry cores such mixtures are shaped and then baked to increase their strength so that they are capable of withstanding any force to which they might be subjected duringV casting. The binders used for these mixtures are In addition to this troublesome coating, the used foundry sand is further contaminated with sand fines, clay, metal and other foreign materials, all of which must be removed before the sand is suitable for re-use,

It is an object of this invention to provide an efficient and economical continuous process for converting used foundry sand into relatively clean sand, free of contarninants and suitable for use alone or. with virgin sand for making foundry Vcores and molds.

'Another object is to provide an' improved process for reclaiming used foundry sand which includes a novel method for scrubbing the sand particles to remove the coating of binder deposited on the surface thereof.

It is a further object to provide a process in which the scrubbing of the used sand is accomplished by abrasion of a slurry of said sand in admixture with a portion of reclaimed sand which has been recycled through the scrubber.

Another object is to provide an eicient method for continuously scrubbing used sand which comprises employing as an abrasive in the scrubber recycled sand from which nes, clay and carbonaceous surface films, which normally function as a lubricant between sand particles, have been removed.

Other objects and advantages of our process will become apparent from the following description of our invention taken in conjunction with the accompanying drawings in which:

Figure 1 is a diagrammatic representation of apparatus suitable for practicing the continuous process of the invention, and

Figure 2 shows a portion of the apparatus of Figure l, which has been somewhat modified.

Mold and core sand which has been previously broken up to granular size and from which tramp metal has been removed by conventional magnetic means is charged continuously into primary classifier 10, together with water supplied through pipe 12. The Vclassifier consists of a cylindrical vessel having a conical bottom with a discharge claimed) sand which has been discharged from the tert l n l'rvatentedMar. 5, 19.57

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opening therein connecting to pipe 20 containing a lvalve 18. A funnel 14 is centrally disposed within the cylinder near the upper open end thereof with its" restricted end connected with a drain conduit 16 extending in a generally downward direction and piercing `vthc wall of the vessel 10. The used sand and water introduced into the classifier forms a slurry or ilowable mixture. The sand fines, clay, and other more buoyant foreign materials float to the surface and are carried by the overflow stream into the funnel'14 and are discharged from the conduit 16 to Waste. The slurry of the heavier sand particles ows by gravity from the primary classiier 10, through conduit 20j and into a scrubber 22. The scrubber consists of a tankl or container 24 having-an impeller 28 driven by a rnotor 26 disposed in the lower central part of the tank.y An overiiow spout or chute 30 located in the wall of the tank nearthe top thereof provides for discharge of the scrubbed sand. Reference is hereby made to Patent No. 2,637,3304

for a further detailed description of this apparatus and its function.

Up to this point the process is similarto these known and previously disclosed. However, instead 'of following the usual procedure of agitating the used sand alone we' depart from standard practice by recycling to thcslurry in the scrubber, a portion of the partially scrubbed ,(ref

minal point of the apparatus. The source Yof this sand and its treatment prior to discharge .into the scrubber will be explained hereinbelow. We have found that by vigor-` ously agitating the used sand slurry'in the Vpresence of added reclaimed sand, the greater proportion of which is sharp and free of surface coating, the contaminating coat-1v ing of carbonfclay, fines and organic binder remaining adhered to the used sand deliveredpfr-om the primary clas` silier is much more effectively removed in considerably shorter time. Adhered contaminating coatings function as a lubricant between the grains' and 'reduce the electiveness of the sand vgrains as an abrasive. Hence, reclaimed' sand, from which the coating has been at least partially. removed, is superior in abrasive action-to' sand which still' bears the contaminating coating.

- Circulation of the4 slurry within the` scrubber dueto agitationl by the impellerZS-causes discharge of sand par" ticles, free of contaminating coating, from a spout or chute 30 into pumping tank 32. Make up water may be added to tank 32 as required to reduce the sand .to pumping consistency, through water line 34. The sand pump 36 in line 38, which connects the pumping tank 3.2 to a secondary classifier 40, lifts the slurry of cleaned sand grains, together with the loose particles of contaminating coating removed therefrom, to the secondary classifier. This classifier is of the hydraulic counterow type and comprises a cylindrical tank 41 terminating in a tapered discharge tube 44. A spreader tiume 42 over the entrance opening of the tank 41 causes the incoming material to be distributed evenly over the surface of the tank. The lower end of the tapered tube 44 is surrounded by an annular ring 46 which is adapted to direct jets of water from valved supply line 48 into the tube. The water lloivnsupwardly continuously, counter to the slurry of incoming sand particles, and contaminating particles and other foreign material removed therefrom in the scrubber. The velocity of the upwardly owing stream is adjusted so as to carry the lighter contaminating particles and foreign material to the surface from which they llow to waste through spillway 50. Only cleaned sand grains larger than a predetermined size are permitted to discharge by gravity through the tapered tube 44. The opening in the end of tube 44 is relatively small in cross section so that the ow of water and'sand therethrough is less than the tlow of material into the classifier; thus a substantially constant rate of overflow of water and contaminating material into the spillway 50 is assured.

The lower end of the discharge tube 44 connects t-o a closed reservoir or container 60 having a conical bottom and two valved discharge conduits 62 and 64 leading therefrom. Conduit 62y delivers reclaimed sand slurry to the scrubber 24 for` purposes previously pointed out. The remainder of the output of reclaimed sand slurry is delivered to a centrifuge 66 or other dewatering device for removal of most of the water, and then to -a drier in which the balance of the water is evaporated. Dry, cleaned sand discharged from the drier is ready for use in preparing foundry cores and molds.

If, for some reason, the valves in outlet conduits 62 and 64 must be closed temporarily, and the incoming material more than fills the reservoir 60, water will rise in the pipe 63 and be discharged into the trough 50 to waste.

'In a modification of the invention shown in Figure 2 the top of the reservoir `60 is open. The discharge tube 44 from classifier 40 is equipped with a valve 45. In this embodiment, the ow of material into the reservoir 60 may be controlled by adjusting the valve 45 anywhere from fully open to fully closed.

Hence, slurries ofincoming material normally discharged from classiiier 40 in volume sufiicient to overflow reservoir 60 may be held back by means of valve 4S, with the overflow being discharged through the trough 50.

It will be noted that recycled sand is being continuously separated from the ne particles of adhered coating removed therefrom as the sand moves from the scrubber to the secondary classifier, and back to the scrubber. We have found that for eicient continuous operation of the process itis desirable yto discharge a maior proportion of the scrubbed sand slurry back into the scrubber, p referably from 70 to 90%, with the remainder being removed for use. The amount of sand recycled will vary with the source of the used sand, some being more .diliicult to scrub than others. For example, sand used with iron castings requires about .87 to 8.8% recycle for eiffective scrubbing, while that used for steel requires only about 75% recycle sand. The formulation of the core or mold sand compound will also aiect the amount of recycling necessary. Generally, the more tenaciously the contaminating coating is adhered to the .used sand, the longer it will have to .be scrubbed; and consequently, the larger the proportion .of `sand that must be recycled.

area51;

The ow of sand and water mixture through the apparatus is rapid and continuous, thus keeping the sand in suspension at all times so that it can be handled eiciently in the various pieces of equipment comprising the present apparatus.

It will be understood kthat the embodiments of the invention shown in detail herein are illustrative only and are not intended as a deiinition of the scope of the invention, reference being had for this purpse to the appended claims.

What is claimed is:

1. A process for reclaiming used foundry sand which comprises forming a owable slurry of said sand in water, separating the more buoyant sand fines and contaminants from the heavier sand particles in Vthe slurry, adding cleaned reclaimed sand to said slurry and agitating thc resulting mixture to scrub said heavier sand particles free of the contaminating coating thereon. separating the freed coating from the slurry and evaporating the Water from the slurry to provide dry clean sand.

2. A continuous process for reclaiming used foundry sand which comprises charging said sand and water into a primary classifier to form a owable slull'lvr and ,to separate the more buoyant sand nes and contaminants from the heavier sand particles, passing the slurry of heavier particles through a scrubber to separate by abrasion from said particles the contaminating coating adhered thereto, passing the Vslurry mixture of scrubbed sand and freed contaminating particles into a secondary classifier for removing the contaminating particles therefrom, collecting the slurry of scrubbed sand in a reservoir, recycling a major proportion of said sand through said scrubber to serve as the abrasive in scrubbing the contaminated sand, and discharging a minor proportion of said sand to a drier to dry the sand for reuse.

3. The process of claim 2 in which 70 to 90% o f the reclaimed sand is recycled through said scrubber.

References (ited in the nl@ of this patent UNITED STATES PATENTS 2,383,045 Den Breejen et al Aug. 2l, `1945 2,477,948 Allen Aug. 2, 1949 2,478,461 Connolly Aug. 9, 1949 2,480,748 Luce et al, Aug. 30, 1949 2,637,330 Webster May 5, 1953 

